Legal Question in Family Law in California

There is nothing illegal about it but you can get an order to have them returned.

Mr. McCrary is correct. Also, however, if you do not do something about it and she stays there for six months, California will lose jurisdiction over the children and any legal proceedings affecting them, including a divorce, will have to proceed in the other state. So if you need to take legal action you should take it within six months of when they left unless you want to litigate in the other state.